The present invention relates to an optical disk in which information is recorded both on land and groove tracks.
The invention also relates to an optical disk drive device using such an optical disk.
More particularly, the invention relates to recognition patterns used for recognition of the header part provided in front of each information sector.
In conventional phase-change type optical disks, data is recorded only on grooves, and lands serve to guide the light spot for tracking, and to reduce crosstalk from adjacent groove tracks. If data is recorded on lands as well, the track density can be doubled on condition that the width of the grooves and the width of the lands are both unchanged. It has been discovered that the crosstalk between adjacent land and groove tracks is reduced if the difference in height between the lands and grooves is .lambda./6 (.lambda. being the wavelength of the light source). Because of this discovery, the use of both land and groove tracks has become feasible. The use of both land and groove tracks is also advantageous with regard to the ease of mastering of the disk: it is easier to attain a certain recording density by the use of both land and groove tracks than by reducing the track pitch using only the groove tracks.
For instance, in the case of optical disks for use as computer data files, optical disks in which data is recorded both on land and groove tracks, and the tracks are concentric, so that after recording of one revolution (on a groove track, for example), a track jump is effected to start writing on the adjacent track (a land track). Sectors are managed in accordance with the sector addresses. Accordingly, the operation for recording and reproducing data, such as computer data, which need not be continuous, can be carried out without difficulty.
Rewritable optical disks are however also used for recording continuous data such as motion picture, or music. In multimedia applications (where computer data and video and audio data are mixed), spiral tracks, as in compact disks, may be preferred because of the continuity of the tracks.
In this case, the tracks need to be formed into a spiral form rather than a concentric form. However, in an optical disk in which the information is recorded both on lands and grooves and the tracks are spiral, it is necessary, after tracing the entire spiral formed of all the land tracks, for example, and groove tracks, to jump from the end of the land track spiral to the beginning of the groove track spiral. It is then necessary to access from the inner periphery to the outer periphery of the disk. Such an operation is time-consuming. In a disk which is divided into annular zones, the track jump is made from the inner periphery of the zone to the outer periphery of the zone, and the time for the jump is shortened but there is still a similar problem.
FIG. 23A and FIG. 23B show details of the header region 4 in a conventional optical disk wherein data is recorded on both groove and land tracks. FIG. 23A shows the case where headers are provided separately for the land and groove tracks, and addresses dedicated to the respective tracks are formed. FIG. 23B shows the case where headers are provided on an extension of a boundary between land and groove tracks, and each address is shared by the land track and the groove track separated by the boundary. In either case, the headers include address pits.
The header portion is formed of embossments (dents or projections) physically formed for representing the address information and the like of the sector preceded by the header, the sector being a unit for recording data. Specifically, pits having the same height as the lands, or pits having the same depth as the grooves are formed in the header portion where no tracks are formed.
There are several methods for forming prepits suitable for the land/groove recording configuration. Two principal ones are those shown in FIG. 23A and FIG. 23B.
In the configuration shown in FIG. 23A, dedicated prepits are provided for each sector of the land or groove track. Because the dedicated prepits can record various items of information, such as the one indicating whether the sector following the dedicated prepits is in a land track or a groove track, control in the optical disk drive device is facilitated. However, the width of the prepits must be sufficiently narrower than the track width. This means that the laser beam used for forming the tracks cannot be used for forming the prepits, and the fabrication of the medium is difficult.
In the configuration shown in FIG. 23B, the prepits are shared by the land and groove tracks adjacent to each other. The prepits can be formed by using the same laser beam as that used for forming the tracks, and by shifting the laser beam by 1/2 of the track pitch laterally of the track, i.e., in the radial direction of the disk. However, during writing or reading of the disk, the shared prepits cannot indicate whether the sector following the prepits is in a land track or groove track, so that the optical disk drive device must have a means to find whether a land track or groove track is being traced by the light spot, and the control in the optical disk drive device is difficult.
In the above-described optical disk allowing recording and reproduction, it is also necessary to solve the problem of the track offset. This relates to the fact that the one beam-and-push-pull method is used for the tracking, rather than a three-beam method. This is because the recording requires a greater laser power. Also, in the case of pit-forming recording, such as the one on a write-once disk, the side spots (used in a three-beam method) causes a disturbance to the tracking operation.
In a push-pull tracking, the tracking error is detected using the diffraction distribution of the light spot illuminating the pregrooves as shown in FIG. 24, and fed to the servo system, so that offset may occur due to the eccentricity of the disk or tilting of the disk. More particularly, an optical head 10 has a laser diode 66 emitting a laser beam, which is passed through a half-mirror 65 and an objective lens 67 to illuminate an optical disk 8 rotated by a disk motor 9. The reflected light beam from the light spot on the disk 8 is guided by the objective lens 67 and the half-mirror 65 and is received by a photodetector 11, and the tracking error is detected using the diffraction distribution of the light spot on the optical disk 8. The detected tracking error is used to control an actuator coil 64 for driving the objective lens 67.
For instance, a tilt of 0.7 degrees or an eccentricity of a 100 .mu.m (equivalent to lateral movement of the objective lens 62 of 100 .mu.m as indicated by broken lines in FIG. 24) causes shifting of a light distribution 12 on the photodetector 11, and hence an offset of 0.1.mu..
To prevent such a phenomenon, a drive device having higher mechanical and optical accuracy is used, and various other contrivances are adopted.
FIG. 25A shows the method of mirror surface correction in which a mirror surface part 7 is used. FIG. 25B shows the pit configuration of the optical disk used in combination with the wobble pits correction method.
In this method, wobble pit pits 68 and 69 being shifted in the radial direction of the disk by 1/2 of the track pitch are used. These methods are described in the following publications:
(1) Ohtake, et al. "Composite Wobbled Tracking in the Optical Disk System," on pp. 181-188 in Optical Memory Symposium '85, held on Dec. 12-13, 1985, published by Optical Industry Technology Promotion Association, PA0 (2) Kaku, et al. on "Investigation of compensation method for track offset," pp. 209-214 in Optical Memory Symposium '85, held on Dec. 12-13, 1985, published by Optical Industry Technology Promotion Association.
FIG. 26 shows a track offset correction circuit used in combination with a disk having the mirror surface portion 7 shown in FIG. 25A. A split photodetector 70 detects the tracking error by a push-pull method. An adder 15 adds the outputs of the two half-portions of the split photodetector 70 to produce a signal indicative of the total amount of light received, which corresponds to the total amount of light reflected from the disk. A differential amplifier 16 determines the difference between the outputs of the two half-portions of the split photodetector 70, to produce a signal indicative of the tracking error. A mirror surface detector 20 detects the mirror surface portion 7. A sample-hold circuit 23 samples and holds the tracking error signal when the light spot passes the mirror surface portion 7, and holds the sampled value as an offset information. A differential amplifier 47 determines the difference between the tracking error signal and the offset information. The output of the differential amplifier 47 indicates the tracking error having the offset removed.
FIG. 27 shows an offset correction circuit used in combination with a disk having wobble pits shown in FIG. 25B. A wobble pit detector 22 receives the output of the adder 15, and detects the wobble pits, i.e., produces a signal to a sample-hold circuit 23 when the light spot passes the wobble pit laterally shifted toward one side of the track, and produces another signal to a sample-hold circuit 24 when the light spot passes the wobble pit laterally shifted toward the other side of the track. Responsive to these signals (i.e., when the light spot passes the wobble pits 68 and 69), the sample-hold circuits 23 and 24 sample the output of the differential amplifier 16, and holds the sampled value. A differential amplifier 27 determines the difference between the outputs of the sample hold circuits 23 and 24, as an offset. An adder 28 adds the tracking error signal obtained at the differential amplifier 27 to the tracking error signal obtained by means of the ordinary push-pull method, to produce the tracking error signal from which the offset has been removed.
FIG. 28 illustrates the control characteristics for the case where a tracking error signal obtained by wobble pits and the tracking error signal by means of the conventional push-pull method are both used. GI denotes a tracking open loop characteristic by means of the conventional push-pull method, and G2 denotes a tracking open loop characteristic by means of the wobble pits.
In this configuration, the guide grooves are discontinuous or interrupted at the mirror surface portion 7. With this configuration, a correction circuit for correcting the mirror surface offset, shown in FIG. 26, is required. The signals output from the two half-portions of the split photodetector 70 are input to the differential amplifier 16, which thereby produces a tracking error signal. The sum signal produced by the adder 15 is supplied to the mirror surface detector 20, which thereby generates a timing signal indicating the timing at which the light beam passes the mirror surface portion, and hence the signal should be sampled. The tracking error signal .DELTA.T produced by the differential amplifier 16 includes an error component .DELTA.Tg (error due to the photodetector 70 and the differential amplifier 16), a true tracking error .DELTA.Ts, and an offset component .delta. due to various causes including the tilting of the disk, so that it is given by: EQU .DELTA.T=.DELTA.Ts+.DELTA.Tg+.delta. (1)
The sample-hold circuit 23 samples the tracking signal at the mirror surface portion 7, and holds the sampled value for each sector. The output of the sample-hold circuit 23 represents .DELTA.Tg+.delta.. Accordingly, in view of the equation (1), subtracting the output of the sample-hold circuit 23 from the output of the differential amplifier 16 at the differential amplifier 47 results in the true tracking signal .DELTA.Ts. In this way, a closed-loop servo system for achieving an accurate track following can be formed.
Another method of correction is a method using wobble pits. According to this method, a pair of sequences of pits shown in FIG. 25B are formed by alternately deflecting the light beam, using ultrasonic deflector, during fabrication of the original disk for mastering. During recording and reproduction, the amounts of the reflected light received when the light spot is passing the wobble pits on the respective sides are compared, to detect the tracking error. Specifically, a differential amplifier 27 shown in FIG. 27 determines the difference between the outputs of the sample-hold circuits 23 and 24 to obtain the tracking error. As shown in FIG. 29, when the light spot passes along a line closer to the center of the pit 68 on one side (top side in FIG. 25B) than to the center of the pit 69 on the other side (bottom side in FIG. 25B), an output signal illustrated by the dotted line is obtained. When the light spot passes along a line closer to the center of the pit 69 on the bottom side than to the center of the pit 68 on the top side, an output signal illustrated by the solid line is obtained. The difference obtained by subtracting the signal (amount of received reflected light) obtained when the light spot is passing the wobble pit 69 at the back, from the signal (amount of received reflected light) obtained when the light spot is passing the wobble pit 68 at the front, represents the magnitude of the tracking error and the direction of the tracking error. This means that the position at which the light spot passes is detected. Compared with the method relying on the diffraction distribution due to pre-grooves, the above-described method realizes a better servo system.
Another tracking method has been proposed, in which the feature of the above-described wobble pit method is maintained, and which is compatible with systems using conventional push-pull tracking method. The sector configuration in this system is composed of an index field with pre-pits shown in FIG. 23B, and data field which the user later utilizes. The index field is provided with address information, as well as wobble pits which may or may not serve also as a sector detection mark, and pre-grooves for tracking.
With such a configuration, the true tracking error is detected from the wobble pits, and the offset used in the push-pull tracking can be corrected. In this case, the open-loop characteristic of the tracking servo is such that the gain for tracking on the basis of the wobble pits is relatively large in the low-frequency region, and the gain for the tracking on the basis of the push-pull method is relatively large in the high-frequency region, as shown in FIG. 28. As a result, data can be recorded and reproduced, while the light spot is maintained on the center of the track, regardless of the drive device used, and compatibility between the recorded disk and the drive device can be preserved.
With the above-described optical disk drive device, information is recorded on lands and grooves to increase the recording density. In such an optical disk, to avoid the complexity of operation during disk-mastering, it was necessary to provide address pits in the header portion, being 1/2 pitch shifted in the radial direction from the information track, so as to enable reading during tracing of the land track or groove track. Each header is therefore shared by the land and groove, whether the light spot is scanning a land or a groove is not known from the address alone.
The sequences of pits for recording the address information are disposed at positions shifted with respect to the track center, so that when the signal amplitude is lowered or track offset occurs, it is difficult to obtain information reliably. In particular, when the address information is incorrectly read, the recording and reproduction of information over the entire sector cannot be achieved, and fundamental information as to whether the light spot is scanning a land or a groove, or in which zone the light spot is scanning, or the like may become incorrect, and the disk rotation control, tracking control, or the like may fail.
In the case of a disk of a spiral configuration in which a land and a groove alternate every revolution, it is necessary to judge whether the sector following the header is in a land or a groove. This judgment must be reliable, since if this judgment is erroneous, failure of tracking may occur.
Furthermore, because the tracking polarity is reversed every revolution, the polarity of the tracking error signal is reversed every revolution, and error in counting using the tracking error signal during track access, or failure in pull-in at the time of track jump may occur.
In addition, during access, when the boundary between adjacent zones is not known, CLV (constant linear velocity) control is effected after tracking onto the target track, so that the settling requires time. To avoid this problem, a detecting means which can detect the tracking polarity and the current zone position even when tracking is not attained.